Single-electron devices have very low power consumption, and hence can relatively improve the degree of integration of circuits as compared to conventional devices. In particular, the single-electron devices have significantly special characteristics in that a drain current is increased or decreased periodically depending on a gate voltage.
More specifically, when induced charges are increased in a quantum dot due to an increase in the gate voltage and consequently the quantity of induced charges in the quantum dot reaches an elementary charge quantity, one electron tunnels from a source to the quantum dot to cause the quantity of induced charges to be cancelled so as to minimize a potential energy of the quantum dot. Like this, through the sweeping of the gate voltage, a phenomenon is repeated periodically that the quantity of induced charges of the continuous values in the quantum dot increased by the gate voltage are cancelled by the electron tunneling from the source to the quantum dot to minimize the potential energy of the quantum dot. This phenomenon is called a coulomb oscillation. That is, the coulomb oscillation is observed by the periodic on/off of the drain current according to a change in the gate voltage. In the coulomb oscillation, a coulomb blockade region and a tunneling region are regularly oscillated so that signals “1” and “0” are periodically generated for respective regions.
The single-electron device is a device that enables one electron is added to the electrode or is subtracted from the electrode by a coulomb blockade effect. The single-electron device has low power consumption and appears as the next-generation device to substitute for a complementary metal-oxide-semiconductor (CMOS) in terms of the degree of integration.
Currently, the operating temperature of the device is increased in such a fashion that the electric capacity is reduced through only a reduction in the size of a single quantum dot. But, if multiple quantum dots are formed by using metal dots, the electric capacity of the single-electron device itself can be decreased to raise the operating temperature of the device to the roan temperature. When the multiple quantum dots are arranged in series, the number of quantum dots having the same electric capacity is increased to decrease the entire electric capacity.
In general, the main use purpose of silicide is as follows. As a design rule of semi-conductor devices is more strictly applied, high sheet resistance of a gate is a main cause of degrading the operating speed of the device. Thus, in order to improve the operating speed of the device, it is indispensable to fabricate a gate electrode of low resistance. For the purpose of such improvement of resistance, a gate electrode was used which includes a refractory metal silicide having a low specific resistance.
Although not shown concretely, the aforementioned conventional single-electron device can be shown in the following two types. One type is that after formation of a channel, the quantum dots are formed by a thermal oxidation process depending on the shape of the channel. In order to fabricate a room temperature-operating device employing this scheme, a quite small quantum dot is required and it is not easy to control the electric capacity of a tunnel junction, which makes fabrication of the device difficult.
The other type is that a plurality of quantum dots is formed serially on a single substrate by means of electronic beam lithography and reactive ion etching (RIE) to reduce the entire electric capacity of the quantum dots. In order to fabricate the roan temperature-operating device employing this scheme, the size of a single quantum dot is made large, and hence the length of an active region is increased up to a range of a μm unit, which makes it difficult to improve the degree of integration of the single-electron device.